How to Set Up a Video Camera for the Analysis of Movement (week 3)

Question 1

state the 4 main steps of the overall process

Answer 1

1. prepare your participant
2. set up your camera
3. calibrate the area you will analyse
4. record your trials

Question 2

what do you do to prepare your participant (first step)

Answer 2

place reflective markers on bony landmarks of the lower limb in order to analyse joint angles of the lower limb

Question 3

what are the 5 bony landmarks on the lower limb that you place reflective markers on (first step)

Answer 3

1. 5th metatarsal joint of the foot (lateral)
2. lateral malleolus of the ankle (lateral)
3. femoral epicondyle of the knee (lateral)
4. greater trochanter of the hip (lateral)
5. iliac crest of the pelvis (lateral)

Question 4

there are 7 steps to setting up your camera for video analysis, state the first 4

Answer 4

1. get tripod ready - adjust legs so camera height is in the middle of desired performance (eg - hip for full body)
2. attach camera to tripod via base plate which attaches to the camera
3. place camera/tripod perpendicular to plane of motion you will record
4. pan (L+R), roll (L+R tilt), and tilt (F+B tilt)

Question 5

there are 7 steps to setting up your camera for video analysis, state the final 3

Answer 5

5. zoom into participant + focus camera on something they’re holding (eg - paper saying focus) + then zoom back out
6. press shutter button + change shutter speed
7. adjust aperture (iris button) - higher F-stop = smaller aperture (visa versa)

Question 6

state 2 things about calibrating the area required for analysis (step 3)

Answer 6

1. scale the video to get coordinate data from pixels

2. record participant holding a known length object both horizontally + vertically for 3 seconds each video

Question 7

state 3 things about recording your trials (step 4)

Answer 7

1. use the remote to avoid touching the camera and accidentally adjusting the set up
2. ensure the whole movement in recorded (i.e. - film 2 seconds pre + post)
3. record enough trials for proper analysis

Question 8

how and why do you adjust the shutter speed ? (4 points)

Answer 8

1) press the shutter button on the side of the camera
2) rotate the thing at the front left of the camera to change the shutter speed to 1/1000 for fastest movements, 1/200 for walking
3) faster movements require higher shutter speeds to avoid blurring of the movements, but there will be less light as the sensor is exposed to light for shorter durations
4) you could artificially add light digitally, but this could add ‘noise’ to the image, making it look grainy

Question 9

how and why do you adjust the aperture ? (5 points)

Answer 9

1) press the ‘iris’ button on the side of the camera
2) can rotate the thing at the front of the camera to adjust aperture
3) higher aperture = more light = smaller F-Stop number = shallower depth of field
4) press the button again to set it to auto (white box)
5) there should be enough light in the lab to set it to the auto setting

Question 10

how and why do you calibrate the video ? (4 points)

Answer 10

1) calibration allows us to scale our video to get co-ordinate data from the pixels
2) calibrate with a meter stick with a spirit level to ensure that its level
3) record 2 short videos with the tool in the horizontal and vertical planes
4) this allows us to scale x and y co-ordinate data

Question 11

what 2 things do you need to remember when recording your trial ?

Answer 11

1) use the remote to avoid toughing the camera and off-setting the set-up
2) record enough time before and after the movement trial to ensure the whole motion is captured

Question 12

how and why do you focus the camera ? (4 points)

Answer 12

1) zoom into the participant holding a sign
2) zoom in and focus in on the text on the sign as that is where the movement is going to occur
3) rotate the front of the camera to change the focus to get to greatest clarity and sharpness
4) then zoom back out again to the desired field of view